We plan to better define the in vivo role of cytotoxic activated macrophages in resistance to cancer by capitalizing on observations made in earlier work on this project. We found that pretreatment of cytotoxic activated macrophages with trypan blue inhibited their in vitro cytotoxic function. Subsequently, we noted that trypan blue treatment of mice inhibited nonspecific tumor resistance induced by BCG as well as specific tumor resistance. In the proposed work we plan to determine if, in addition to inhibition of macrophage cytotoxic function, trypan blue affects other immunologic and nonimmunologic components of host response. To determine if trypan blue is a selective inhibitor of the cytotoxic function of activated macrophages, we plan to perform a number of studies which will assay the effect of this azo dye on skin graft rejection, antibody response to sheep red blood cells, nonspecific mitogen-induced lymphocyte stimulation, specific mitogen-induced lymphocyte stimulation, footpad and skin-delayed hypersensitivity responses, MIF production, T-lymphocyte killing of specific target cells, macrophage chemotaxis, as well as other responses related to host defense.